1. Field of the Invention
The invention concerns a method and a medical image acquisition device to evaluate a time series, in particular of two-dimensional images of a contrast agent flow in at least one blood vessel of the human body within the scope of a test bolus measurement, wherein the acquisition of the time series begins with administration of the contrast agent.
2. Description of the Prior Art
Contrast agent-enhanced magnetic resonance tomography is a known examination method to show the arterial or venous vessel system. A contrast agent that intensifies the signal of the blood vessels relative to the surrounding tissue is administered. By data acquisition before and after administration of the contrast agent, the surrounding tissue can be almost completely eliminated by subtraction. In this imaging method the most significant requirement is to synchronize the contrast agent administration exactly with the data acquisition so that the contrast agent bolus passes through the image region during the data acquisition. In order to prevent an overlay of the arteries by the veins, it is additionally required that the data acquisition be ended before the enrichment of the contrast agent in the veins (return flow).
For this purpose it is known to acquire a time series of approximately 40-80 (in particular two-dimensional) individual images with an image repetition rate of one image per second, typically, synchronized with the injection of a reduced quantity of contrast agent (known as a test bolus) before the actual, diagnostic image acquisition, in particular a magnetic resonance image acquisition. The image series itself is frequently also designated as a “test bolus”. The two-dimensional images of the time series do not need to be acquired in the target area of the subsequent diagnostic image acquisition itself; rather, they can be acquired from a location in the subject remote from the administration location, such that ideally the enrichment in the arteries and the return flow through the veins (and thus also the suitable time window in the target area) can be determined. For example, an acquisition of the time series in the neck region can be used for the subsequent examination of the blood vessels in the head.
An optimally exact determination of the arterial and venous contrast agent course—in particular in the form of a contrast agent course curve—decisively determines the image quality of the image acquisition that is ultimately to be implemented. The images of the time series are therefore typically manually evaluated in a post-processing step. First arteries and veins are determined in the images of the time series. This requires the user to navigate through the time series in order to identify the blood vessels. For example, if a point appearing suitable to the user is first selected, an algorithm extracts the contrast agent course curve and provides this information to the user.
This procedure is disadvantageous because the segmentation of particularly small blood vessels is time-consuming and error-prone. Depending on the vessel pathology, not all blood vessels in a test bolus time series are equally well suited for evaluation.